Oxidation and reduction of glycolic and glyoxylic acids in plants. II. Glyoxylic acid reductase.

Clagett, Tolbert, and Burris (1) discovered an enzyme of wide-spread occurrence in the green parts of many plants which catalyzes the oxidation of glycolic and L-lactic acids. The enzyme, which was partially purified from tobacco leaves, seemed to catalyze the oxidation of glycolic acid, through glyoxylic acid, to formic acid and CO, (2). In view of the possible importance of glycolic acid oxidase in the metabolism of higher plants, work was undertaken to obtain further information on the mechanism of action of the enzyme and its biological significance. The enzyme has been isolated from spinach leaves in a highly purified form and has been found to be a flavoprotein with FMN’ as prosthetic group. Glycolic acid oxidase is, to the best of our knowledge, the first flavin enzyme isolated from higher plants. The enzyme catalyzes the oxidation by molecular oxygen of glycolic and L-lactic acids to glyoxylic and pyruvic acids, respectively, with the production of hydrogen peroxide. In the absence of catalase, the peroxide reacts non-enzymatically with glyoxylic or pyruvic acid t,o yield formic or acetic acid, COS, and water. Kun (3) has recently found glycolic acid oxidase in mammalian liver and has obtained evidence that the enzyme is a flavoprotein. Further work has revealed the presence in spinach leaves of an enzyme which catalyzes the reduction of glyoxylic to glycolic acid by reduced pyridine nucleotides. The new enzyme, for which the name glyoxylic acid reductase is suggested, has been partially purified. In the presence of catalytic amounts of glyoxylic or glycolic acid, a mixture of glyoxylic acid